Rolling composite magnesium-base alloy sheets



Jan. 2, 1945.

H. A. DIEHL ET AL 2,366,185

ROLLING COMPOSITE MAGNESIUM-BASE ALLOY SHEETS Filed May 4 1942 Magnesium base a/loyabeer Magnesium base alloy .s/wez r Sheefs 40% *0 75% reduced in i'hicknesa and bonded foye/ber INVENTORS Harold A. Die/ll BY Johi'i G. McDorla/a' ATTORNEYS s Patented Jan. 2, 1945 ROLLING COMPOSITE MAGNESIUM-BASE ALLOY SHEETS Harold A. Diehl, Bay City, and John C. McDonald, Midland, Mich., assignors to The Dow Chemical Company, Midland, Mich., a corporation of Michigan Application May 4, 1942, Serial No. 441,728

3 Claims.

This invention relates to an improved method of bonding together sheets formed of magnesium or plastically deformable magnesium-base alloys.

posite sheets are known, but none provides a bond between the two sheets which is strong enough to withstand without rupture the severe stresses to which the sheets sometimes are subjected during fabrication and use.

An object of the present invention, then, is to provide an improved method of making composite articles formed of magnesium and a magnesium-base alloy or of two or more different magnesium-base alloys in which the individual sheets forming the article are held together by a firm strong bond capable of resisting all stresses to which such articles are ordinarily subjected.

The accompanying drawing shows in Fig. l a cross-section of a pair of magnesium-base alloy sheets tack welded at the edges, and Fig. 2 is a similar view of the same sheets on being pressed between a pair of rolls of a, rolling mill.

Bonding of magnesium-base alloy sheets according to the invention is accomplished by roll ing together the sheets at a temperature between 750 and 900 F. and at a rate of reduction in thickness'of at least 40 per cent per pass through .the rolls. The generation of heat and the mechanicalworking accompanying the rolling appear to cause an interaction, possibly a diffusion of metal, between the twoadjacent' surfaces, and thus t form a firm strong bond between the sheets.

In practice, the magnesium or magnesium-base alloy sheets are first'carefully cleaned to remove mill scale, organic matter, and any chemical finish which may be present, preferably by sanding. The clean sheets to be bonded are then laid one upon another and are gripped together firmly by mechanical means, as by passing wire or steel tape around the sheet and drawing it tight, or by tacking the sheets together at the edges by welding as shown inFig. 1. The resulting stack of two or more sheets is then transferred to a scope:

suitable oven and heated to a temperaturein the range 750 to 900 F., preferably above 800' F.

The hot pack of sheets is then removed from the oven and passed once or preferably several times through a conventional rolling mill adjus'ted to produce a reduction in thiclmess of the pack per pass of at least 40 per cent, reductions in the range 40 per cent to 75per cent per pass being preferred as shown in Fig. 2. After the rolling step, the wires or other securing means may be removed from the pack. The original sheets constituting the pack are found to be bonded together firmly. The composite article thus formed may then be subjected to further rolling and annealing operations as desired to develop any range of physical characteristics of whichthe metal is capable, and may be cut, punched, drawn, or otherwise shaped without danger of rupturing the bond between the original sheets.

In so far as is known, the process of the invention may satisfactorily be applied to bonding magnesium or any plastically deformable magnesium-base alloy to any other plastically deformable magnesium-base alloy. As a practical matter, however, the invention finds its greatest application in bonding high strength magnesiumbase alloys containing aluminum in a proportion up to 10 per cent as the major alloying element to highly corrosion resistant magnesium-base alloys containing manganese in a proportion up to 2 per cent as the major alloying element. In this way there is formed a composite article having a high strength core and surfaces of high corrosion resistance.

The following example will illustrate the invention but is not to be construed as limiting its Example A 0.47 x 8 x 8 inch extruded slab of Dowmetal FS (a magnesium-base alloy containing 2.7 per 'being substantially magnesium) were carefully cleaned by sanding The cleaned sheets were then superimposed with the thick sheet in the middle and were secured together by welding along the edges. The resulting pack was then placed in a furnace and heated to a temperature of 900 R, after which the heated pack was passed repeatedly between rolls at a rate of reduction in thickness per pass of 50 per cent with reheating to temperature between passes until a final thickness of 0.075 inch was reached. 'The composite sheet thus produced exhibited a firm tight bond between the individual sheets of which it was formed.

Other modes of apply mgthei priiiciple of the" invention may be employed instead or" those explained, change being made as regards the details described, provided the steps recited in any 7 01 the following claims or the equivalent thereof' are used.

We claim: 1 1. The method of bonding together sheets formed of magnesium or plasticallydeformable I magnesium-base alloys which comprises rolling the unbonded sheets togetherat a temperature between 750 and 900 F. at the rate of reduction in thickness of at least 40 per cent per pass through the rolls.

"e-method of bonding together sheets formed of different plasticallyji deformable mag- .nesium-base alloys which comprises superimposing the sheets to be bonded, heating them to a temperature in the range 750 to 900 F.,, and passing the heated unbondedhsheets together through rolls at a rate of reduction in thick-; ness per pass of at least 40 per cent.'

' 3. The method of bonding a sheet formed of a plastically deformable magnesium-base alloy containing aluminum in a proportion-up to 10 

